This invention relates to radiant energy manipulation, collection, redirection and concentration. More particularly, this invention relates to the use of a totally internal reflecting (TIR) lens used to capture and redirect light from an extended light source such as a neon or fluorescent lamp.
TIR elements are well known and have been proposed for use in a variety of applications. For example, U.S. Pat. No. 4,337,759 (Popovich et al.) describes the design and use of TIR lenses for various technologies including photovoltaic cells, thermoelectric cells, thin films, lasers, photochemical, solar power and other means which use radiant energy. Further, U.S. Pat. No. 5,404,869 (Parkyn, et al) discloses improvements in the design of such lenses including the use of curved faceted TIR surfaces instead of using a flat surface for better collimation, focusing, and increased design freedom. Additionally, the ""869 patent discloses a lens that redirects light from the source onto a spot in front of the lens giving more efficient focusing and brightness.
One of the asserted uses of such a lens is in conjunction with an aspheric lens for elimination of some illumination non-uniformity typical of earlier TIR lenses, making it particularly useful in imaging projectors, light emitting diodes (LED), optical fibers, spectrophotometers, and toroidal lamp reflection in a forward orientation good for battery powered fluorescent lights.
In addition, U.S. Pat. No. 5,577,493 discloses an apparatus comprising a TIR lens plus a xe2x80x9clight ray deviatorxe2x80x9d positioned along the light path between the source and the TIR lens, for deviating light toward portions of the lens spaced from the axis, thereby more evenly distributing light flux at the TIR lens. The improvement was thought to be useable with liquid crystal displays (LCD) to enhance the incandescent light sources ability to illuminate uniformly. Moreover, U.S. Pat. No. 5,613,769 (Parkyn et al.) discloses a TIR lens having non-circular configuration around an optical axis that is asserted to be suitable for holographic diffusers and lenticular lenslet arrays to produce tailored output intensities useful for compact LED light sources. It also discloses TIR facets in a lens increasingly separating in one arc and increasingly converging in a second arc, a lens where the perimeter is non-circular, or rectangular, or square, thus creating what is described as axe2x80x9cmushroom lens.xe2x80x9d Such lenses are said to provide a powerful way of controlling the light beam, with improved collimation as the result of the entire beam having the same angular spread resulting in improved propagation.
In general, although the use of TIR lenses began with efforts to concentrate light, in particular, solar energy, for various uses, developmental efforts in the field are now directed toward uses in light emitting devices and the concentration and focusing of light from low energy sources in a highly efficient manner for illumination purposes. Perhaps one of the most significant improvements exemplified by use of a TIR lens is that one can focus light from a source nearly 90 degrees from the target, whereas use of a traditional refraction based lens would limit the angle from source to target to only about 30 degrees. This development allows the design of lamps or collectors with significantly higher efficiencies.
Unfortunately, however, the prior art relating to the use of TIR lenses with a neon or fluorescent lamp are based on an array of facets which capture light from the source through one face of the facet (the entry face) and then internally reflect it off the other face, thus redirecting the light to the target zone or viewer out an exit face of the lens. In each case, the side of the facet from which the light is reflected appears bright to the target zone or viewer, while the entry face of the facet appears dark. So, for an entire circular lens surface covering a lamp, for example, the light would appear to the target zone or viewer as a series of concentric bright rings separated from each other by a series of concentric dark rings. The bright rings are the result of viewing the light leaving the TIR facet at the reflecting face and directed toward the viewer or target. The dark rings are the result of the light entering the TIR facet. Such a pattern is reminiscent of the series of light and dark lines seen as a result of passing light through a Fresnel lens. The ring effect can be lessened by increasing the number or density of facets in the TIR lens, thereby decreasing the thickness of the lines or rings, but cannot be eliminated. Any attempt to increase the facet density to compensate for this problem results in higher tooling costs and construction complexity. Further, the increased density also results in a loss of efficiency of the lens due to the increased tip effects at the point of each TIR facet.
Another problem encountered with the use of conventional TIR lenses to focus light concerns their efficiency. In order to maximize the focusing power of TIR lenses, it is necessary to construct the lens in such a manner as to catch the incident light not directly in front of the lens. This is normally accomplished by either curving or xe2x80x9cwrapping aroundxe2x80x9d the lens, and by the addition of alternate reflecting means to bounce the light from the source traveling away from the TIR lens back toward the lens. Such curvature or additional reflectors may not be desirable from a design point of view when a flat or uniformly curved lamp surface is desired.
Co-pending, co-assigned U.S. Ser. No. 09/112,564 has disclosed one approach for alleviating this problem by integrating optical elements into the lamp. The above improvements notwithstanding, there continues to be a need for a TIR lens which allows for focusing of light without creation of the alternating dark/light concentric ring pattern, and which simultaneously allows for the construction of such a TIR lens with a flat or uniformly curved surface. These needs are met by the invention described herein.
The present invention provides a TIR lens that efficiently focuses light without the creation of light/dark concentric rings, and which can be used in the form of a uniformly curved or flat surface. These two advantages are accomplished by using TIR facets which collect light from two different sources simultaneously. Consequently, from the viewer""s angle, the light directed does not have concentric rings and is uniformly bright across the surface of the lens. Moreover, the lens can be manufactured so that it has either a flat, smooth or uniformly curved surface. Further, the TIR lenses of the present invention allow the light to be focused and gathered with high efficiency.
The improvements over the prior art are accomplished by each TIR facet having two reflecting faces which can capture light from two different sources; unlike the prior art facets having a reflecting and a refracting face. The angle defined by the two faces of the TIR element is dependent on the angle of the desired incident light which is being redirected, and is similar in that regard to prior art TIR elements. By appropriate selection of this angle, the brightness of the light is extended across the refractive element and both faces of the TIR facet in a uniform manner.
The improved facets are preferably used in conjunction with closely spaced radiant energy sources placed proximally to the entry faces of the lens apparatus. The radiant energy sources may be oriented either linearly (parallel to each other), circularly (toroid), or could in fact, be arbitrarily oriented with respect to the lens elements. The radiant energy sources may be mounted or otherwise disposed on a support, or they may be formed within a support substrate such as discharge channels formed in a glass substrate which is filled with a noble gas. One particularly useful method for forming a device in which the radiant energy source is formed within a support substrate is that described in co-pending, co-assigned U.S. Pat. No. 5,858,046. As described therein, such discharge channels are vacuum formed into a sheet of glass material in the desired shape or orientation, and a second sheet of a similar material applied on top of the first sheet to seal the discharge channels. The two sheets may then be sealed together by the application of heat and/or pressure. The heat may be residual heat in the glass or it may be added subsequently from an extrinsic source. Using this method, a series of parallel channels, or a continuous serpentine discharge channel, can be formed in virtually any configuration, including 3-dimensions, for containing a radiant energy source.
The TIR lens apparatus may be laid on top of, or located proximally to the support containing the radiant energy sources, and is oriented so that a single TIR facet is located between each pair of radiant energy sources, and a refractive element is located directly above each radiant energy source. In a preferred embodiment, the distance between radiant energy sources or discharge channels is equal to the distance between TIR elements, and the range of this distance is approximately from about 1 to 3 cm. This distance range is not the maximal limit, as the distance is generally a factor of the size and weight of the lens being constructed. Accordingly, it would be theoretically possible to construct a lens where the TIR elements were spaced centimeters or even hundreds of centimeters apart depending on the size of the apparatus and light sources. The limitation to the magnitude of the lens size is generally due to the weight and construction of the lens material and not as a result of an optical limitation. Further, the distance between each radiant energy source and the interposed TIR element is preferably the same. to preserve a symmetrical appearance. This arrangement will allow the TIR elements to capture and reflect the radiant energy from two different sources and redirect it across the exit face of the lens with uniform brightness.
In an alternate embodiment, the lens and the radiant energy source may be constructed out of a single piece of glass or laminate material. In this embodiment, discharge channels may be vacuum formed into one surface of a sheet having the TIR facets formed on its opposite surface such that a discharge channel is interposed between each pair of TIR facets. A second sheet of glass comprising refracting elements corresponding to the locations of the discharge channels may then be laid down on top of the formed channels opposite the TIR facets, and the two sheets then sealed together by the residual heat of formation of the first sheet and the application of pressure as needed to both sheets simultaneously. The material for this one-piece lens apparatus would preferably be made out of a non-porous transparent material, such as glass, in order to maintain the radiant energy source, e.g. a suitable noble gas, within the discharge channels of the lens.